Data structure for flash memory and data reading/writing method thereof

ABSTRACT

A data structure for a flash memory and data reading/writing method thereof are disclosed. A 512 bytes data and a redundant code derived from the data encoded with a 6-bit error correcting code scheme are stored in a first sector and a second sector with sequential address in a block of the flash memory respectively. A logic block address information of this block is divided into two parts that are stored in the first sector and the second sector respectively.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of U.S. application Ser. No.12/122,768, filed May 19, 2008, which claims priority to TaiwanApplication No. 096118884, filed on May 25, 2007.

FIELD OF THE INVENTION

The present invention relates to a data structure applied for flashmemory and data reading/writing method thereof, and more particularly toa data structure comprising a redundant code which includes 6-bit errorcorrecting code (ECC) and data reading/writing method thereof.

BACKGROUND OF THE INVENTION

Flash memory has become a very popular data storage apparatus nowadays.However, the data stored in flash memory may become erroneous due tooccasional electrical noise, or due to random, non-repetitive bitarrangement in memory cell caused by the limited access speed as aresult of the material characteristic of the flash memory. To maintainthe correctness of the data stored in the logic memory cell, additionalchecking codes composed of bits are usually inserted into the data forlocating and correcting the error bit(s). This data protection scheme iscalled error correction code (ECC) checking.

FIG. 1 a illustrates a schematic view of the data structure of a flashmemory in accordance with the conventional art. The flash memory 1comprises a plurality of blocks 11, each block 11 comprises a pluralityof pages 12 each composed of at least one sector 13, and each sector 13comprises at least a data area 131 and a spare area 132. Because theminimum transmission data amount of the typical Integrated DeviceElectronic interface (IDE-ATA) is 512 bytes, the storing space of thedata area 131 is generally 512 bytes and the storing space of the sparearea 132 is 16 bytes.

FIG. 1 b illustrates a schematic view of the data structure of the sparearea 132 of the flash memory in accordance with the conventional art.The spare area 132 comprises bad memory information 141, ECC checkinginformation 142, logic block address (LBA) information 143, split blocklogic sector address (SBLSA) information 144, and a redundant code 145for ECC. The redundant code 145 is derived from the data by encodingwith certain ECC scheme.

Generally, the storing space of the bad memory information 141 is onebyte, which comprises bad block information and bad page information.The bad block information is for indicating whether this block is adefective block and the bad page information is for indicating whetherthis page is a defective page. The storing space of the ECC checkinginformation 142 is one byte, and the ECC checking information 142 is forindicating whether the ECC checking should be executed. The storingspace of the logic block address information 143 is two bytes. Thestoring space of the split block logic sector address information 144 istwo bytes. The storing space of the ECC redundant code 145 is 10 bytes.

The flash memory in accordance with the conventional art is commonlyencoded with a 4-bit ECC scheme to generate a 10-byte redundant code,which can then be stored in the data structure illustrated in FIG. 1 b.Because data protection attracts much attention, using an ECC schemewith more bits becomes a trend of designing flash memory. However, sincethe redundant code of a 6-bit ECC scheme requires a storing space of 15bytes, the redundant code of the 6-bit ECC scheme cannot be stored inthe conventional data structure as illustrated in FIG. 1 b. What isneeded is then to dispose a data structure with stronger data protectionand error correction ability in a limited storing space of the flashmemory.

SUMMARY OF THE INVENTION

Therefore, it is one objective of the present invention to provide adata structure applied for flash memory and data reading/writing methodthereof for a more efficient data protection scheme in the limited spaceof the flash memory.

In an embodiment of the present invention, a data structure applied fora flash memory is provided to store a 512 bytes data and a redundantcode in a first sector and a second sector which are two neighboringsectors in a block of flash memory respectively. The redundant code isderived from the data encoded with a 6 bits ECC scheme. The logic blockaddress information of this block is divided into two parts which arestored in the first sector and the second sector respectively.

In an embodiment of the present invention, a data reading method appliedfor a sector of the flash memory which includes a data, an ECC checkinginformation and a redundant code, comprises following steps of:

-   -   i) performing an ECC decoding process on the data based on the        redundant code;    -   ii) determining whether the ECC decoding process is completed,        and outputting the processed data if the ECC decoding process is        completed;    -   iii) determining whether the number of stored byte sequence with        a predetermined value in the data exceeds a threshold value if        the ECC decoding process can not completed;    -   iv) marking the sector to be an erased sector if the number of        stored byte sequence with predetermined value in the data        exceeds the threshold value; and    -   v) determining whether this sector has uncorrectable error or        this sector is an erased sector based on the ECC checking        information if number of stored byte sequence with the        predetermined value does not exceed the threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

A general architecture that implements the various features of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention. Throughout the drawings, reference numbers are re-used toindicate correspondence between referenced elements. In addition, thefirst digit of each reference number indicates the figure in which theelement first appears.

FIG. 1 a illustrates a schematic view of the data structure of a flashmemory in accordance with the conventional art;

FIG. 1 b illustrates a schematic view of the data structure of the sparearea of the flash memory in accordance with the conventional art;

FIG. 2 illustrates a schematic view of the data structure of a flashmemory in accordance with an embodiment of the present invention;

FIG. 3 illustrates a flow diagram of the data writing method inaccordance with an embodiment of the present invention;

FIG. 4 illustrates a flow diagram of the data reading method inaccordance with another embodiment of the present invention;

FIG. 5 illustrates a schematic view of a flash memory with split blockstructure; and

FIG. 6 illustrates the flow diagram of the operation process of theinventive data structure when applied to split block structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a data structure for flash memory anddata reading/writing method. While the specifications describes severalexample embodiments of the invention, it should be understood that theinvention can be implemented in many ways and is not limited to theparticular examples described below or to the particular manner in whichany features of such examples are implemented.

Referring to FIG. 2 for a schematic view of the data structure for flashmemory in accordance with an embodiment of the present invention, thesector 201 and the sector 202 are two neighboring sectors, wherein thesector 201 includes a data area 21 and a first spare area 22, and thesector 202 includes a data area 23 and a second spare area 24. Thestoring space of the data area 21 or the data area 23 is 512 bytes, andthe storing space of the spare area 22 or the spare area 24 is 16 bytes.

Since when a 6-bit ECC scheme is applied for encoding data, the storingspace required by the generated redundant code is 15 bytes, and only onebyte of space for storing other information is left for each of thefirst spare area 22 and the second spare area 24 after storing theredundant code. Because the remaining space is too small to store otherinformation for each sector separately, in the present invention suchother information is then stored using jointly the remaining spaces ofthe two neighboring sectors.

In this embodiment, the first spare area 22 is used for storing bad pageinformation 221 of one bit, ECC checking information 222 of one bit, badblock information 223 of one bit, the first the logic block addressinformation 224 of five bits, and the ECC redundant code 225 of fifteenbytes. The second spare area 24 is used for storing bad page information241 of one bit, error checking information 242 of one bit, second logicblock address information 244 of six bits, and ECC redundant code 245 offifteen bytes.

A complete logic block address can be obtained by combining the firstpart of the logic block address information 224 and the second part ofthe logic block address information 244. The ECC redundant code 225 andthe ECC redundant code 245 are derived from the data encoded with a6-bit ECC scheme.

Referring to FIG. 3 for a flow diagram of a data writing method inaccordance with an embodiment of the present invention, the method isapplied for writing data into a sector of a flash memory and includesthe following steps of:

Step 30: receiving the first data and the second data, each requiring astoring space of 512 bytes.

Step 31: encoding the first data and the second data with the 6-bit ECCscheme, to generate the first redundant code and the second redundantcode. The storing space required by each of the first redundant code andthe second redundant code required is fifteen bytes.

Step 32: selecting the first sector and the second sector which are twoneighboring sectors in the block, obtaining the bad page information andthe bad block information of the two sectors, and setting the ECCchecking information for the two sectors.

Step 33: dividing the logic block address information of this block intoa first logic block address information of 5 bits and a second logicblock address information of 6 bits.

Step 34: storing the first data, the first redundant code, the firstlogic block address information, the bad page information, the bad blockinformation, and the ECC checking information into the first sectorbased on the data structure illustrated in the sector 201 of FIG. 2.

Step 35: storing the second data, the second redundant code, the secondlogic block address information, the bad page information, the bad blockinformation, and the ECC checking information into the second sectorbased on the data structure illustrated in the sector 202 of FIG. 2.

When reading data from the flash memory, the sector storing data may bein one of the following three statuses:

1. Data has been written in this sector, and the data can be decoded andcan be successfully read out.

2. Data has been written in this sector, but the data cannot be decodedand cannot be successfully read out.

3. This sector is an erased sector and has not been written with data.

Generally, whether this sector has been written with data can bedetermined by examining the ECC checking information stored in thesector, and the redundant code can be then used to check whether thedata stored in the sector is correct. However, the data structure of thepresent embodiment uses only one bit to store the ECC checkinginformation, and it is at all possible that data corruption occurs atthe bit for storing the ECC checking information. As a result of theaforementioned, relying only upon the one-bit ECC checking informationcan easily lead to false judgment. The data reading method of thepresent invention described below can reduce the probability of falsejudgment.

Referring to FIG. 4 for a flow diagram of an embodiment of the datareading method in accordance with an embodiment of the presentinvention, the method includes the following steps of:

Step 40: reading the data and the redundant code stored in a sector andperforming an ECC decoding process on the data based on the redundantcode, for error-checking and correcting the data.

Step 41: determining whether the ECC decoding process is completed. Ifthe ECC decoding process is completed, proceed to step 42. If the ECCdecoding process is not completed, proceed to step 43. If the number oferror bits detected exceeds what the ECC scheme can tolerate, the ECCdecoding process is considered failing.

Step 42: outputting the corrected data.

Step 43: determining whether the number of stored byte sequence withvalue of “0×ff” exceeds a threshold value. If this number does exceedthe threshold, proceed to step 44; if this number does not exceed thethreshold, then proceed to step 45.

Step 44: marking this sector to be an erased sector.

Step 45: determining whether the ECC decoding process should beperformed to this sector based on the ECC checking information stored inthis sector. If the ECC decoding process should be performed, proceed tostep 46; if the ECC decoding process should not be performed, thenproceed to step 44.

Step 46: marking this block as having uncorrectable error.

Preferably, the flash memory mentioned above can be Multi Level Cell(MLC) or Single Level Cell (SLC).

Referring to FIG. 5 for a schematic view of the flash memory with splitblock structure, the flash memory 5 has a split block structure andincludes the first block 51 and the second block 52, and the secondblock 52 serves as a data buffer. When data is to be written in thefirst block 51, it will first be written in the second block 52. Thedata stored in the second block 52 will then be sequentially written inthe first block 51 when the second block 52 becomes full. Due to thenature of flash memory data access, the writing speed of the flashmemory can become faster by using the split block structure. Forexample, as illustrates in FIG. 5, when the user wants to write datasequentially in page 11, page 32 and page 2, under the split blockstructure these data are first stored in the second block 52, and thesedata are then later written in page 11, page 32 and page 2 of the firstblock 51 according to the order of the page location when the secondblock 52 becomes full.

Because under the split block structure, the data temporarily stored inthe second block 52 must further record additional location informationregarding where the data is to be stored in the first block 51, it isthen unsuitable to adopt the 6-bit ECC scheme in encoding the datatemporarily stored in the second block 52.

Referring to FIG. 6 for a flow diagram of the operation process of theflash memory with split block structure in accordance with an embodimentof the present invention, this operation process is performedcorresponding to the flash memory 5 illustrated in FIG. 5, and includesthe following steps of:

Step 60: receiving data to be written in the first block 51.

Step 61: encoding the data with a 4-bit ECC scheme and then storing theencoded data, the redundant code generated from the encoding process,the location information where the data will be stored in the firstblock 51, and related parameters into the second block 52.

Step 62: checking if the second block 52 is full. If the second block 52is full, proceed to step 63; if second block 52 is not full, proceed tostep 60.

Step 63: sequentially reading unprocessed page data from the secondblock 52, and performing the ECC decoding process on the encoded databased on the redundant code in this unprocessed page data, for checkingand correcting the data.

Step 64: encoding the data with an 6-bit ECC scheme, and then storingthe encoded data, the generated redundant code, and other relatedparameters into the first block 51 based on the data structureillustrated in FIG. 2.

Step 65: checking whether the data in the second block 52 are entirelyprocessed. If the data in the second block 52 is entirely processed, endthe flow process; if the data in the second block 52 are not entirelyprocessed, proceed to step 63.

While the invention has been described by way of example and in terms ofa preferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

1. A data reading method applied for a sector of a flash memory, saidsector storing a data, an ECC checking information and a redundant code,and said method comprising the steps of: (a) performing an ECC decodingprocess on said data based on said redundant code; (b) determiningwhether or not said ECC decoding process is completed, and if said ECCdecoding process is completed, outputting said processed data, and ifsaid ECC decoding process is not completed, proceeding to step (c); (c)determining whether a number of instances of a stored byte sequence witha predetermined value in said sector exceeds a threshold value, and ifsaid number does exceed said threshold value, marking said sector to bean erased sector, and if said number does not exceed said thresholdvalue, proceeding to step (d); and (d) determining whether said sectorhas uncorrectable error or said sector is an erased sector based on saiderror checking code.
 2. The data reading method of claim 1, wherein saidflash memory is Multi Level Cell or Single Level Cell.
 3. The datareading method of claim 1, wherein said predetermined value is 0xff.